It is well known to mount display monitors above eye-level in informational and advertizing applications, such as accommodation information kiosks, airline flight information displays, and interactive menu displays. For maximum effectiveness, such displays should be highly viewable, especially in brightly lighted environments.
FIG. 1 shows a prior art vertical, or "straight" screen display mounted at or near ceiling level in a typical viewing application. It is well known that image brightness it a key viewability factor and that the human perception of image brightness is affected by the image contrast, i.e., the higher the image contrast, the brighter it appears. Moreover, the brightest viewing angles for displays are in a "best viewing cone" having an axis that is normal to the screen. Unfortunately, using a straight screen directs the best viewing cone over the head of the viewer and, to make matters worse, reflects ambient light off the vertical screen and down toward the viewer, which reduces the image contrast and "washes out" the display, giving a perception of reduced brightness.
As shown in FIG. 2, prior workers have attempted to solve this problem by simply slanting the screen downward, and in some applications it viewability is improved. However, in interactive menu display applications, where graphic images and text are intermixed, viewability and text readability are of upmost importance and simply slanting a conventional cathode-ray tube ("CRT") display is often unsuitable. In particular, text readability typically requires high display resolution and a relatively large screen size, such as a 38 inch diagonal, to display readily readable textual characters at eight to 12 foot viewing distances. CRT displays having such resolutions and screen sizes are simply too heavy and bulky for wall or ceiling mounting. CRT display disadvantages include the possibility of causing lifting injuries to service personnel, mounting shelf or bracket size and strength requirements, lack of service accessibility, and extension distance from the wall.
Slanting CRT displays downward to increase their viewability often complicates the wall mounting and service access problems, and increases the extension distance from the wall.
If These are serious problems in the emerging market for interactive menu displays in fast food restaurants. Such displays must mount above and behind the serving counter in existing, brightly illuminated, relatively shallow spaces, previously occupied by conventional static menu boards. Moreover it is preferable that an array of such displays be mounted side-by-side to form an elongated "banner" display that combines animated display advertizing with interactive menus for each serving station. Of course, displays in fast food restaurants must also be highly reliable, compact, clean, well ventilated, readily serviceable, and affordable. Down time for any reason detracts seriously from profitability.
There are previously known techniques for employing various kinds of display technologies in "video walls" and signage applications. Multiscreen displays employ an abutted array of substantially identical display devices that each display a subdivided portion of a total image such that together they display the total image. Because multiscreen displays require that each of the display devices be perceived as part of a whole large display device, it is important to make the boundaries between adjacent display devices appear as inconspicuous as possible. Unfortunately, the human eye is very sensitive to boundary discontinuities, making an acceptably "seamless" multiscreen display very difficult to produce. CRT-based multiscreen displays also have image stability and image matching problems that only make the problems worse.
Many of the above-stated problem can be mitigated by employing digitally addressed, compact, lightweight displays, based on those described in copending U.S. patent application Ser. No. 08/740,966, filed Nov. 5, 1996, for COLOR AND LUMINANCE CONTROL SYSTEM FOR LIQUID CRYSTAL PROJECTION DISPLAYS, which is assigned to the assignee of this application and incorporated herein by reference. However, the liquid crystal display ("LCD") projection systems described therein are more suitable for floor-standing video wall applications because they are heavy, have protruding legs, large straight screens, are vertically stackable, and have front and rear service access. Unfortunately, these features render them generally unsuitable for elevated wall mounting. Moreover, such LCD projection systems have a large internal fold mirror for projecting the image on the projection screen. If the projector is mounted in a elevated position, the fold mirror produces a first surface reflection from the ambient room lighting to the screen, further washing out the projected image.